Mitt Romney is struggling to get everyday people to give small amounts to his campaign. For Barack Obama, the problem is attracting big bucks from wealthy donors.

Romney’s small-dollar fundraising continues to trail the efforts of John McCain at this point in the 2008 campaign, despite a populist fundraising boom from last month’s Supreme Court decision on Obama’s health-care law. Obama, meanwhile, is depending more heavily on small-dollar donations, and raising more, than he did in his record-breaking 2008 campaign. But he is attracting far fewer donors who give the legal maximum to his campaign than he did at this point in 2008.

A new report by the Campaign Finance Institute illustrates how the two candidates are raking in cash from radically different sources. Through the end of June, Romney had raised $22.4 million in aggregate donations of less than $200 per donor, or 15% of his total haul. By comparison, John McCain had raised $25.9 million from donors who gave less than $200, or 21% of his total haul, at the same point in 2008. But in total, Romney has raised $155.3 million, well ahead of the $144.1 million that McCain had raised at this point, largely by attracting more donors who give the maximum amount of $2,500 to his campaign. “Small donors are typically people who are pretty excited,” explains institute executive director Michael Malbin, the author of the report. “The Romney campaign has been very slow in exciting a mass base.”

Romney’s struggles come in a political environment that is significantly improved for Republicans from 2008, and despite a campaign apparatus that is better organized and more stable than the one McCain had at this point four years ago. A recent poll by Gallup found that 51% of Republicans say they are more excited than usual for the coming election, up from 35% at the same point in 2008. At the same time, the share of excited Democrats has plunged from 61% to 31%.

The Obama campaign’s small-dollar fundraising operation has not been hurt by that drop in enthusiasm, at least in comparison with 2008. He has raised $112 million from under-$200 donors, compared to $93.6 million at this point in 2008. But enthusiasm among well-heeled donors is another matter. At this point in the last election, Obama had raised $87.3 million from donors who had given the legal limit, 27% of his total haul. This year, Obama has only raised $47 million in maxed-out donations, or 16% of his total.

So which candidate has more to worry about? It’s hard to say at this point. Romney’s superior ability to attract donors able to part with $2,500 will be a major asset, given the fact that changes in campaign finance laws allow those same donors to write even bigger checks to outside groups like super PACs, which can run ads in support of Romney’s election. By contrast, Obama’s broad support among l0w-dollar donors could suggest an extensive network of motivated backers who may give the President a grassroots advantage in organizing.

If Romney is able to win the election without much small-dollar success, his victory could call into question the viability of the online fundraising model that Obama pioneered in 2008. It is also possible that he finds a way to tap into the broader public sentiment over the coming months. Donations from people who had given less than $200 nearly doubled from $4.1 million in May to $9.9 million in June, helped in part by the Supreme Court decision upholding Obama’s health-care reform, which the campaign effectively turned into rallying cries. In the coming weeks, Romney is expected to announce his Vice Presidential nominee, providing both campaigns with another news peg for raising money in small amounts.